A number of exhaust system components of conventional jet engines as well as other hot exhaust washed structures are fabricated from titanium alloys. While titanium alloys have a number of advantageous material properties, the exhaust system temperatures of next generation jet engines are anticipated to reach a level at which components fabricated from titanium alloys may have an unsatisfactory service life. In this regard, the historical trend has been for each generation of jet engine to exhaust gasses having greater temperatures than the prior generation in an effort by the engine designers to achieve greater thermodynamic efficiency. However, at the exhaust system temperatures predicted for the next generation of jet engines, such as temperatures in excess of 1,000° F., exhaust system components fabricated of titanium alloys, such as exhaust system nozzles and exhaust system centerbodies as well as other hot exhaust washed structures, may oxidize relatively rapidly, thereby disadvantageously reducing the service life of the components.
A number of conventional exhaust system components, such as exhaust system nozzles and exhaust system centerbodies, have been constructed in the form of a honeycomb core sandwich. In this regard, these exhaust system components can include a pair of titanium alloy face sheets disposed on opposite sides of a honeycomb core, which may also be formed of a titanium alloy. In order to reduce the noise emanating from an engine, some of the exhaust system components may include Helmholtz resonators. In order to provide Helmholtz resonators, perforations or other holes may be defined, such as by drilling, through the titanium alloy face sheet which is adjacent to the high-speed flow of exhaust gasses. The perforations or other holes defined by the titanium alloy face sheet open into respective cells of the honeycomb core. By appropriately tuning the geometry of the honeycomb cells, the noise emanating from the engine may be advantageously reduced.
In an effort to provide exhaust system components and other hot exhaust washed structures that can withstand higher temperatures, such as temperatures in excess of 1,000° F., components comprised of high-temperature metal alloys have been proposed. However, these high-temperature metal alloys, such as Inconel 718, Rene 41 and Columbium alloys, are undesirably heavy relative to comparable components fabricated from titanium alloys. Since the weight of an aircraft, including its engine, is a key concern relating to both the performance and cost of operation of the aircraft, the use of exhaust system components and other hot exhaust washed structures formed of high-temperature metal alloys that are heavier than corresponding titanium alloy components have not proven to be a desired solution.
Accordingly, it would be desirable to provide exhaust system components, such as nozzles and centerbodies, as well as other hot exhaust washed structures which can withstand exhaust gas temperatures in excess of 1,000° F. without any meaningful reduction of the service life of the components. Additionally, it would be advantageous to provide exhaust system components, such as nozzles and centerbodies, and other hot exhaust washed structures which can withstand such higher exhaust gas temperatures, but which weigh no more than corresponding titanium alloy components so as to not increase the weight of the engine.